PASADENA, Calif.—In the next decade, when scientists are able to study Earth-sized worlds around other stars, they may find that foliage on some of the planets is predominantly yellow—or orange, or red. It all depends on the color of the star the planet orbits and the stuff that makes up the planet's atmosphere.

That's the conclusion of researchers from the Virtual Planetary Laboratory, a NASA-funded initiative at the California Institute of Technology, who are announcing today results from a series of comprehensive computer models for guiding the future search for plant life on other worlds. Two related papers on what to expect out of photosynthesis are being issued in the journal Astrobiology.

Determining the range of possible colors is important because scientists need to know what to look for when they begin getting spectra of light from faraway Earth-sized planets, says lead author Nancy Kiang, a biometeorologist at NASA's Goddard Institute for Space Studies, and currently a visitor at Caltech's Spitzer Science Center.

"The dominant color of photosynthesis could be yellow, or orange, or maybe red," Kiang explains. "I think it is unlikely that anything will be blue—and, of course, green plants are also a possibility, since that's what we have here."

"What makes this study unusual is the highly interdisciplinary method by which planetary scientists, atmospheric scientists, biologists, and others have pooled their efforts in modeling the possible spectra of light available to plants on Earth-like planets orbiting around other stars," says Vikki Meadows, an astrobiologist at Caltech and lead scientist of the Virtual Planetary Laboratory. Because the study requires data about everything from the type of photons given off by a main-sequence star in a particular stage of its life, to the depth of water that an aqueous plant might prefer, a huge variety of information is required.

"No single astronomer or biologist or atmospheric scientist could have attacked this problem individually to get the simulation," says Meadows, who is herself an astrobiologist whose original academic training was in astronomy. "So these papers are truly interdisciplinary pieces of work."

The researchers focused on the way plants use light for energy to produce sugar—which is pretty much the definition of photosynthesis—because photosynthetic pigments must be adapted to the available light spectrum. The available light spectrum at a planet's surface is a result of both the light from the parent star and filtering effects of gases in the atmosphere. For example, ozone absorbs ultraviolet light, so that not much reaches Earth's surface.

"It turns out that the spectrum of the number of particles of light is what is important, and on Earth there are more particles in the red," Kiang explains. "This could explain why plants here on Earth are mainly green."

On Earth, plants absorb blue light because it is energetic, and red light because the photons are plentiful. There is more than enough energy from the blue and red in sunlight, so plants do not really need more. Therefore, they reflect away relatively more green light, which is why plants appear green to us.

A planet orbiting a star with the size and temperature roughly like our sun, and with Earth's particular mix of oxygen and what-have-you, would tend to have plants that like to soak up light in blue and red and less in green. But the situation could be different on other planets, where other colors of the spectrum might predominate. In those cases, another color like red might not be so useful, and the plants would mostly appear red.

There are many other factors, such as the role not only ozone plays but also carbon dioxide and water vapor, how the stellar radiation creates chemical reactions in the atmosphere, whether the star is prone to solar flares, how much water is on the planet, how much light gets to the surface, what gases are produced by the plants themselves, and so on. This is why a complex computer model was necessary.

Also, one might wonder what things could live on a planet with very little ozone, for example, where radiation would be a daily assault on living organisms, and energetic particles from solar winds would be like deadly microscopic bullets. Meadows says the modelers have taken such scenarios into consideration, and they think that there might be a "sweet spot" a few to tens of feet below the surface of the water where life is protected from UV radiation.

"We found that the sweet spot could be up to nine meters underwater for a planet orbiting a star significantly cooler than our sun, and photosynthesis could still take place," she says. "Something with a floatation capability could be protected from solar flares and still get enough photons to carry on."

In short, the new model provides a powerful tool for looking for life on other worlds, Meadows says.

"We once thought that planets around other stars were exceedingly rare," she explains. "But every time telescopes have gotten better, we've been able to find more and more Jupiter-sized planets. So there's no reason to think that there aren't a huge number of Earth- sized planets out there as well.

"We may not find anything like ourselves, but it's possible that bacterial life is prevalent on these Earth-like planets," Meadows adds. "If we have the environment for life to exist, then we think that it's likely that life will emerge in these conditions."

The other authors of the two papers are Antigona Segura-Peralta, Giovanna Tinetti, Martin Cohen, Janet Siefert, and David Crisp, all of the Virtual Planetary Laboratory, Govindjee, of the University of Illinois, and Robert Blankenship, of Washington University.

The Virtual Planetary Laboratory was formed as part of the NASA Astrobiology Institute, which was founded in 1997 as a partnership between NASA, 12 major U.S. teams, and six international consortia. NAI's goal is to promote, conduct, and lead integrated multidisciplinary astrobiology research and to train a new generation of astrobiology researchers.

PASADENA, Calif.—On a campus where scientific research can be pretty challenging for the uninitiated, Mike Brown's search for new bodies in the outer solar system is as refreshingly straightforward as, well, the brightly colored marble spheres that sit on his shelf. Each sphere represents a Kuiper-belt object he has found in the last few years, including Eris, which led to the demotion of Pluto to the status of "dwarf planet."

Brown's approach to science is obviously to the taste of California Institute of Technology students as well, because they recently threw their support behind his nomination for the annual Feynman Prize, which is Caltech's most prestigious teaching honor. The prize is given to a faculty member each year for "exceptional ability, creativity, and innovation in both laboratory and classroom instruction," and is in honor of the Nobel Prize-winning physicist Richard Feynman, a favorite teacher and still a powerful influence on campus 19 years after his death.

"I'm thrilled," Brown said after the award was announced. "I never interacted with Feynman, but the people who have won the award in the past are the teachers I have a huge amount of respect for. So it's a fantastic honor."

Brown becomes the fourteenth recipient of the Feynman Prize, which carries a $3,500 award and an equal raise in salary. Brown is also probably one of the few recipients thus far who didn't personally know Richard Feynman.

Nonetheless, Brown structures his classroom methods in a manner reminiscent of the award's namesake, who was also noteworthy for his fresh and original approach to teaching. Brown says that paying close attention to methodology, and to coming up with the best educational outcome for his students, is the only way to go.

"Teaching is terrifying," he says. "It's the most stressful thing I do. I have given countless presentations over the years about my research, but talking at the Air and Space Museum [which he did in mid-March] is nothing like the classroom experience."

One challenge in teaching is the Caltech culture itself, Brown says. A difficult school for everyone, especially undergraduates, Caltech is legendary for the sheer amount of homework and the high expectations on students. Not surprisingly, the students in turn are themselves very astute and quite capable of discriminating between really effective teaching strategies and mediocre ones.

"Around here, you always feel like you're just keeping your head above water when you lecture students," he says. "You can't teach and not have some off days, and you know all too well when you're having one-it's easy to see when the students are engaged and when they're not.

"I guess that's why I try so hard to teach well—I hate that feeling of knowing the students realize I'm having an off day."

According to Caltech provost Paul Jennings, who announced Brown's receipt of the award at a recent faculty meeting, Brown has been singled out for the award because of "his extraordinary teaching ability, his skill in exciting his students, and his evident caring about his students' learning.

"Mike is first recognized for his contribution to Geology 1, Earth and Environment, which he has taught since spring 2005," said Jennings. "Although he himself is an astronomer, well-known for his discovery of a large object in the outer solar system with a diameter greater than Pluto, the possible 'tenth planet,' he volunteered to teach Ge 1 because he wanted to learn the geology material himself."

Brown says that one of his innovations in teaching the Ge 1 course was a type of homework assignment that required students to travel to nearby Eaton Canyon in order to answer homework problems by observation. One of the students who supported his nomination added that his lecture style is also memorable: "Attending a fun and engaging lecture to break the monotony of core classes was the best part of our day."

In his graduate-level course, "Formation and Evolution of Planetary Systems," Brown is also credited by students for making them feel as if they are part of the scientific process. "We could watch the formation of the solar system unfold in front of us, like a good book that we couldn't put down," a graduate student wrote.

Brown says he loves teaching both the graduate and undergraduate classes. Another assumption he bases his preparations for Ge 1 on is that Caltech's science students can benefit intellectually from a different type of lab experience than the ones they encounter in their major courses.

"Ge 1 is a class for nonmajors," he explains. "At a state university, you often find 'rocks for jocks' courses, which are designed for people who aren't going into science but are just trying to get their degrees. Here, we don't have any nonscientists, so the question is what is going to expand their horizons."

The answer Brown has come up with is that geology for scientists who are not themselves geologists should focus on the field as an observational science. "In geology, you take what you're given-you can't drill to the center of Earth to see what's there, or go back in time to see what happened, so the laboratory experience is different from the one in chemistry or physics or biology."

As for the graduate course, the class is designed to give geologists a bit more physics than they may have had as undergraduates. But like the undergraduate course, Brown has also worried about precisely what experience is likely to be of the most intellectual benefit to scientists working in other fields.

"The graduate course is probably the most intuitively taught physics class on campus," he says. "For me, if you can't talk the equation out, you don't really understand it, so everything in the class is aimed at making the physics accessible to geologists who don't need to get heavily into the theoretical aspects, but really need to understand certain equations to do their work."

The son of a NASA engineer, Brown grew up in Huntsville, Alabama, where the nearby presence of the Marshall Space Flight Center and its legendary director Werner von Braun, as well as the Redstone Arsenal, whetted his appetite for all things space-related. Brown attended Princeton University as an undergraduate, and then changed coasts for a doctorate in astronomy from Berkeley.

As for Brown's reputation as a researcher, one need only read the news to find his name associated with a major discovery. In mid-March, Brown and his graduate students Kristina Barkume, Darin Ragozzine, and Emily Schaller reported in the journal Nature that one of the Kuiper-belt objects Brown previously discovered, 2003 EL61, shows evidence of having been struck by a smaller body 4.5 billion years ago. The discovery is important because it reveals new insights into the dynamics of solar-system formation—knowledge that could help us better understand our own home system as well as systems in those galaxies far, far away.

A faculty member at Caltech since 1997, Brown is currently a professor of planetary astronomy. Among the other classes he has taught are Applications of Physics to the Earth Sciences, Observational Planetary Astronomy, Planetary Interiors, and Introduction to the Solar System.

The Feynman Prize is endowed through the generosity of Ione and Robert E. Paradise, with additional contributions from Mr. and Mrs. William H. Hurt, to annually honor a professor who demonstrates, in the broadest sense, unusual ability, creativity, and innovation in undergraduate and graduate classroom or laboratory teaching. Winners are selected by a committee of students, former winners, and other faculty.

PASADENA, Calif.—In the outer reaches of the solar system, there is an object known as 2003 EL61 that looks like and spins like a football being drop-kicked over the proverbial goalpost of life.

Still awaiting a more poetic name, 2003 EL61 largely escaped the media hubbub during last year's demotion of Pluto, but new findings could make it one of the most important of the Kuiper-belt objects for understanding the workings of the solar system. In this week's Nature, the original discoverer of the body, Mike Brown, announces with his colleagues that an entire family of bodies seems to have originated from a catastrophic collision involving 2003 EL61 about the time Earth was forming.

Brown and his team base their assumptions on similar surface properties and orbital dynamics of smaller chunks still in the general vicinity. They conclude that 2003 EL61 was spherical and nearly the size of Pluto until it was rammed by a slightly smaller body about 4.5 billion years ago, leaving behind the football-shaped body we see today and a couple of moons, as well as many more fragments that flew away entirely.

"Some of these chunks are still in orbit around the sun and very near the orbit of 2003 EL61 itself," says Brown, a professor of planetary astronomy at the California Institute of Technology. "The impact made a tremendous fireball, and large icy chunks of the big object split off and went flying into space, leaving behind a huge ice-covered rock spinning end over end every four hours.

"It spins so fast that it has pulled itself into the shape of an American football, but one that's a bit deflated and stepped on," Brown adds.

A significant part of the finding is that the collision occurred in a region of space where orbits are not very stable. "In most places, things go around the sun minding their own business for 4.5 billion years and nothing happens," says Brown. "But in a few places, though, orbits go crazy and change and eventually objects can find themselves on a trajectory into the inner solar system, where they would be what we would then call comets."

As a consequence, many of the shards probably made their way to the inner solar system, and a few have undoubtedly hit Earth in the past. The study thus provides new ideas about how the solar system evolves, and how comets fit into the big picture.

Brown adds that 2003 EL61 will put on quite a show in about a billion years, if anyone is still around to enjoy it.

"It's a long time to wait, but 2003 EL61 could become by far the largest comet in eons," Brown says. "It will be something like 6,000 times brighter than Hale-Bopp a few years ago."

The other authors of the paper are Kristin Barkume, Darin Ragozzine, and Emily Schaller, all graduate students in planetary science at Caltech.

PASADENA, Calif.—A team of astronomers led by Carl Grillmair of the California Institute of Technology has discovered some puzzling things about a Jupiter-sized planet that passes in front of a nearby star in the constellation Vulpecula.

Both the Grillmair team and groups from NASA's Goddard Space Flight Center and NASA's Jet Propulsion Laboratory are reporting today on their independent findings about two transiting exoplanets. These are the first spectra from planets outside our own solar system, and have been made possible by the NASA Spitzer Space Telescope's unexpectedly keen ability to study nearby stars.

According to Grillmair, an astronomer at Caltech's Spitzer Science Center, the planet studied by his group is named HD 189733b. The planet is about 62 light-years, or 360 trillion miles away from Earth, is about 10 percent larger than Jupiter, and has a "year" that lasts only two days. It orbits the star HD 189733, which is somewhat smaller and slightly redder than our own sun. And unexpectedly, the data doesn't show the presence of water.

"It's surprising," says Grillmair. "According to what the theoreticians tell us, we had expected to see a very structured spectrum that would have a particular shape because of the presence of water in the planet's atmosphere. But what we actually see is a very flat spectrum."

Spectral data is good for determining what's in a star—or planet, for that matter—because different substances can look very different when the light from them is split into separate colors by a prism. Scientists in the 19th century discovered that burning a substance and then looking at its light through a prism was an excellent way of figuring out what was being burned, and roughly the same procedure has been used ever since for finding out about the light-emitting things in the universe.

The problem with exoplanets, however, has been that the light of the star can be billions of times brighter than the planet itself. As a result, astronomers have previously been unable to study the spectra of planets outside our solar system due to the sheer distance and their inability to distinguish planet light from starlight.

"Normally, trying to see a planet next to a star is like trying to see a firefly next to an airport searchlight several miles away," Grillmair explains. "But in the case of our planet and the one being reported by the other teams, you can take the combined spectrum of the star and planet, and then when the planet passes behind the star, take another spectrum. By subtracting the second spectrum of just the star from the first, you can divine the spectrum of the planet itself."

Another key element to this discovery is that the observations are done in the infrared. The contrast between the star and the planet isn't as large in the infrared, so researchers can tease out the infrared spectrum of the planet. It remains impossible, with current technology, to do this in the visible light, even for transiting planets.

As for the apparent lack of water, Grillmair says there are at least four possibilities. First of all, there could really be no water, which he feels is not very likely. Second, there could be some other chemicals in the planet's atmosphere that emit radiation just where water absorbs it, thereby effectively camouflaging the signature of the water. This too seems unlikely. Third, the water could be hidden underneath an opaque cloud layer the Spitzer telescope can't see through. Fourth, a theoretical model suggests that, if the planet is in tidal lock (in other words, is so close to its sun that the same side always faces the same way), the atmospheric temperature profile on the day-side of the planet could be such that spectral features are suppressed.

But whatever the case, Grillmair thinks that a healthy collection of additional data during the Spitzer's final year or two of life could settle the matter—and teach us much about the worlds beyond our solar system.

"We really need more data to hammer this thing and knock down the noise," he says. "There will be 17 eclipses during the next year that will be visible to Spitzer, and I'd really like to look at every one of them."

So far, Grillmair and his team have been able to observe the planet for a total of 12 hours during two eclipses. A nearly tenfold increase in data would allow positive identifications of individual chemical elements, which has not been possible with the data returned so far.

"This type of data will undoubtedly be one of Spitzer's greatest legacies," Grillmair says. "Transiting extrasolar planets hadn't even been discovered when the Spitzer Space Telescope was designed, so this was all unanticipated."

NASA's Jet Propulsion Laboratory, located in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

The other members of Grillmair's team are David Charbonneau of the Harvard-Smithsonian Center for Astrophysics; Adam Burrows of the Steward Observatory; Lee Armus, John Stauffer, Victoria Meadows, and Deborah Levine, all of the Spitzer Science Center; and Jeffrey Van Cleve of Ball Aerospace and Technologies Corp.

The Grillmair team's results will be published in an upcoming issue of Astrophysical Journal Letters. A report on the Goddard Space Flight Center team's study of the transiting exoplanet HD 209458b is being published this week in the journal Nature.

A separate paper by the JPL-led team on HD 209458b has been submitted to the Astrophysical Journal Letters. The JPL team, led by Mark Swain, also includes Caltech's Rachel Akeson and Chas Beichman

PASADENA, Calif.—Geologists have uncovered evidence in the oil fields of Oman that explains how Earth could suddenly have changed 540 million years ago to favor the evolution of the single-celled life forms to the multicellular forms we know today.

Reporting in the December 7 issue of the journal Nature, researchers from MIT, the California Institute of Technology, and Indiana University show that there was a sudden change in the oxygenation of the world's oceans at the time just before the "Cambrian explosion," one of the most significant adaptative radiations in the history of life. With a increased availability of oxygen, the team speculates, single-celled life forms that had dominated the planet for the previous three billion years were able to evolve into the diverse metazoan phyla that still characterize life on Earth.

"The presence of oxygen on Earth is the best indicator of life," says coauthor John Grotzinger, the Fletcher Jones Professor of Geology at Caltech and an authority on sedimentary geology. "But it wasn't always that way. The history of oxygen begins about two and a half billion years ago and occurs in a series of steps. The last step is the subject of this paper."

The key insight was derived when Grotzinger's student Dave Fike, who is lead author of the paper, analyzed core samples and drillings taken at a depth of about three kilometers from oil wells in Oman, which are known to have the oldest commercially viable oil on the planet. The results of carbon and sulfur isotopic analyses from the material led the team to the conclusion that the oceanic conditions that laid down the deposits originally in Oman were quite different from conditions of today.

"You need a very different ocean for these conditions to exist—more like the Black Sea of today, with an upper oxidized layer and lower reduced layer with very little oxygen," says Grotzinger. "The ocean today is pretty well oxidized at all layers, but the ocean before the Cambrian period must have been very different."

When organic matter falls into an ocean that doesn't stir, it becomes deprived of sufficient oxygen and cannot survive as multicellular forms. For this reason, with a limited amount of oxygen, life continued in its single-celled form for the first three billion years.

But about 550 million years ago, according to the team's geologic evidence, the deep ocean began mixing its contents with the shallow ocean, resulting for the first time in a fully oxidized deep ocean.

Characterizing the study as paleoceanography, Grotzinger says the evidence is persuasive because it is so clearly evident in the rock record. Geologists have long believed that the rise of oxygen was a key element involved in the Cambrian radiation, so this discovery really helps solidify that hypothesis.

The oxygen trigger helps account for how life 500 million years ago could have gone from its single-celled existence to the emergence just 10 to 15 million years later of all the metazoan phyla we know today. In short, an abrupt increase in the availability of oxygen may have led to the diversity and complexity of life.

Fike is a graduate student at MIT who is currently in residence at Caltech to work with his professor, Grotzinger, who himself came to Caltech from MIT last year. The other authors of the paper are Lisa Pratt of Indiana University and Roger Summons of MIT.

PASADENA, Calif.—Research by the California Institute of Technology, the University of Southern California, and Indonesian scientists indicates that within the next few decades another big tsunami could flood densely populated sections of western coastal Sumatra, south of those that suffered from the tsunami of December 2004.

Four researchers at Caltech and USC have modeled the dynamics of past and plausible future tsunamis.

They hope that such detailed calculations of tsunami characteristics will speed preparations that could save lives. Their work will appear in the Proceedings of the National Academy of Sciences (PNAS) on December 4.

Kerry Sieh, a professor of geology at Caltech and one of the participants in the study, explained, "When we tell people living along this 700-kilometer section of the Sumatran coast that they will likely experience a big tsunami within the next 30 years, they ask for details. How much time after the earthquake will they have before the tsunami strikes? How big will the waves be? How far inland should they be prepared to run? What areas are likely to suffer tsunami damage? This paper is our first attempt to answer these important questions."

The same big fault, or megathrust, that caused the tsunami of 2004 extends much farther southeastward, beneath the Indian Ocean, just off the southwest coast of Sumatra. Rupture of this section of the megathrust, under the Mentawai Islands, produced two great quakes and tsunamis in 1797 and 1833. Such events appear to recur on average every 230 years.

Samples of coral from the islands show how much these previous quakes lifted the seafloor. The patterns of uplift gave the scientists the information they needed to do computer simulations of the historical tsunamis. Costas Synolakis, director of the USC Viterbi School of Engineering's Tsunami Research Center, says that the impact of the computed 1797 and 1833 tsunamis is consistent with historical accounts.

This consistency increased the scientists' confidence in using the same model to evaluate worst-case scenarios for future tsunamis, which, according to Jose Borrero, lead author of the study, "confirm a substantial exposure of coastal Sumatran communities to tsunami surges." For example, two river valleys near Bengkulu, a coastal city of about 350,000 people, experience flooding that extends up to several kilometers inland.

In the models of future tsunamis, offshore islands appear to shield the larger city of Padang somewhat, but even there the 1797 tsunami reportedly carried a 200-ton English ship into the town, approximately a kilometer upstream, and smaller vessels were carried yet further.

"The population of Padang in 1797 and 1833 was a few thousand," Sieh says. "Now it is about 800,000, and most of it is within a few meters of sea level. We hope that these initial results will help focus educational efforts, emergency preparedness activities, and changes in the basic infrastructure of cities and towns along the Sumatran coast," Adds Synolakis, "The message of the 2004 tsunami has not been lost in the research community. We are trying to be proactive and help prevent a disaster like Aceh in 2004."

This tsunami study is the work of four Southern California researchers. Jose Borrero is a scientist at USC's Tsunami Research Center. Kerry Sieh is the Robert P. Sharp professor of geology at Caltech. Mohamed Chlieh is a postdoctoral scholar at Caltech's Tectonics Observatory. Costas Synolakis is a professor in the department of civil and environmental engineering in the USC Viterbi School of Engineering and director of its Tsunami Research Center.

PASADENA, Calif.—Two and a half billion years ago, when our evolutionary ancestors were little more than a twinkle in a bacterium's plasma membrane, the process known as photosynthesis suddenly gained the ability to release molecular oxygen into Earth's atmosphere, causing one of the largest environmental changes in the history of our planet. The organisms assumed responsible were the cyanobacteria, which are known to have evolved the ability to turn water, carbon dioxide, and sunlight into oxygen and sugar, and are still around today as the blue-green algae and the chloroplasts in all green plants.

But researchers have long been puzzled as to how the cyanobacteria could make all that oxygen without poisoning themselves. To avoid their DNA getting wrecked by a hydroxyl radical that naturally occurs in the production of oxygen, the cyanobacteria would have had to evolve protective enzymes. But how could natural selection have led the cyanobacteria to evolve these enzymes if the need for them didn't even exist yet?

Now, two groups of researchers at the California Institute of Technology offer an explanation of how cyanobacteria could have avoided this seemingly hopeless contradiction. Reporting in the December 12 Proceedings of the National Academy of Sciences (PNAS) and available online this week, the groups demonstrate that ultraviolet light striking the surface of glacial ice can lead to the accumulation of frozen oxidants and the eventual release of molecular oxygen into the oceans and atmosphere. This trickle of poison could then drive the evolution of oxygen-protecting enzymes in a variety of microbes, including the cyanobacteria. According to Yuk Yung, a professor of planetary science, and Joe Kirschvink, the Van Wingen Professor of Geobiology, the UV-peroxide solution is "rather simple and elegant."

"Before oxygen appeared in the atmosphere, there was no ozone screen to block ultraviolet light from hitting the surface," Kirschvink explains. "When UV light hits water vapor, it converts some of this into hydrogen peroxide, like the stuff you buy at the supermarket for bleaching hair, plus a bit of hydrogen gas.

"Normally this peroxide would not last very long due to back-reactions, but during a glaciation, the hydrogen peroxide freezes out at one degree below the freezing point of water. If UV light were to have penetrated down to the surface of a glacier, small amounts of peroxide would have been trapped in the glacial ice." This process actually happens today in Antarctica when the ozone hole forms, allowing strong UV light to hit the ice.

Before there was any oxygen in Earth's atmosphere or any UV screen, the glacial ice would have flowed downhill to the ocean, melted, and released trace amounts of peroxide directly into the sea water, where another type of chemical reaction converted the peroxide back into water and oxygen. This happened far away from the UV light that would kill organisms, but the oxygen was at such low levels that the cyanobacteria would have avoided oxygen poisoning.

"The ocean was a beautiful place for oxygen-protecting enzymes to evolve," Kirschvink says. "And once those protective enzymes were in place, it paved the way for both oxygenic photosynthesis to evolve, and for aerobic respiration so that cells could actually breathe oxygen like we do."

The evidence for the theory comes from the calculations of lead author Danie Liang, a recent graduate in planetary science at Caltech who is now at the Research Center for Environmental Changes at the Academia Sinica in Taipei, Taiwan.

According to Liang, a serious freeze-over known as the Makganyene Snowball Earth occurred 2.3 billion years ago, at roughly the time cyanobacteria evolved their oxygen-producing capabilities. During the Snowball Earth episode, enough peroxide could have been stored to produce nearly as much oxygen as is in the atmosphere now.

As an additional piece of evidence, this estimated oxygen level is also sufficient to explain the deposition of the Kalahari manganese field in South Africa, which has 80 percent of the economic reserves of manganese in the entire world. This deposit lies immediately on top of the last geological trace of the Makganyene Snowball.

"We used to think it was a cyanobacterial bloom after this glaciation that dumped the manganese out of the seawater," says Liang. "But it may have simply been the oxygen from peroxide decomposition after the Snowball that did it."

In addition to Kirschvink, Yung, and Liang, the other authors are Hyman Hartman of the Center for Biomedical Engineering at MIT, and Robert Kopp, a graduate student in geobiology at Caltech. Hartman, along with Chris McKay of the NASA Ames Research Center, were early advocates for the role that hydrogen peroxide played in the origin and evolution of oxygenic photosynthesis, but they could not identify a good inorganic source for it in Earth's precambrian environment.

PASADENA, Calif.- The recent devastations caused by earthquakes in south and southwest Asia, by the Indian Ocean tsunami, and by hurricane Katrina offer dramatic proof that communities all over the world are both unaware of, and unprepared for, natural hazards. Unfortunately, while scientists understand much about these natural hazards, that knowledge commonly is not used to reduce the risks.

"Even though we scientists and engineers often can characterize what will happen, there is a big gap between what we know about nature and how people respond to what we know," says Kerry Sieh, the Robert P. Sharp Professor of Geology at the California Institute of Technology. "Thus, with the enormous growth of the human population over the past half-century, it seems inescapable that natural events will take an ever-increasing toll in lives, well-being and property."

On Wednesday, October 18, Sieh will take a look at a few particular natural disasters and what is being done to mitigate their effects. His talk, "Natural Disasters: What We Know vs. What We Do," is the first program of the 2006-2007 Earnest C. Watson Lecture Series.

The talk will take place at 8 p.m. in Beckman Auditorium, 332 S. Michigan Avenue south of Del Mar Boulevard, on the Caltech campus in Pasadena. Seating is available on a free, no-ticket-required, first-come, first-served basis. Caltech has offered the Watson Lecture Series since 1922, when it was conceived by the late Caltech physicist Earnest Watson as a way to explain science to the local community.

Upcoming lectures in the 2006-2007 series include

o Christopher E. Brennen, Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering, Caltech, on "The Amazing World of Bubbles," November 8.

o Philip T. Hoffman, Richard and Barbara Rosenberg Professor of History and Social Science, Caltech, on "Why Did Europe Conquer the World? How Politics and Economics Created a Comparative Advantage in Violence," December 6.

PASADENA, Calif.—The International Astronomical Union (IAU) today announced that the dwarf planet known as Xena since its 2005 discovery has been named Eris, after the Greek goddess of discord.

Eris's moon will be known as Dysnomia, the demon goddess of lawlessness and the daughter of Eris.

The names are those suggested by the discoverers of the dwarf planet—Mike Brown, a professor of planetary astronomy at the California Institute of Technology, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University, and by the discoverers of the moon—Brown and the engineering team of Keck Observatory where the observations were made.

"Eris is the Greek goddess of discord and strife," explains Brown. "She stirs up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis, all the gods were invited with the exception of Eris, and, enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan War.

"She's quite a fun goddess, really," Brown adds. "And, for the Xena fans out there who are sad to see the name go, Eris appeared in her Latin version of Discordia as a recurring character on Xena: Warrior Princess."

True to its name, the dwarf planet Eris has stirred up a great deal of trouble among the international astronomical community, most recently last month when the question of its proper designation led to a raucous meeting of the IAU in Prague. At the end of the conference, IAU members voted to demote Pluto to dwarf-planet status, leaving the solar system with eight planets.

However, the ruling effectively settled the year-long controversy about whether Eris would rise to planetary status. Somewhat larger than Pluto, the body was formally announced to the world on July 29, 2005. With the August IAU ruling, Eris is the largest dwarf planet.

Eris, about 2,400 kilometers in diameter, was discovered on January 8, 2005, at Palomar Observatory with the NASA-funded 48-inch Samuel Oschin Telescope. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Eris is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope.

Eris is now about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), which means that it is some nine billion miles away at present. On a highly elliptical 560-year orbit, Eris sweeps in as close to the sun as 38 astronomical units. At present, however, it is nearly as far away as it ever gets.

Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year revolution. This means that Eris is sometimes much closer to Earth than Pluto—although never closer than Neptune.

Dysnomia, the only satellite of Eris discovered so far, is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. The name is both a nod to Lucy Lawless, the actress who played Xena on the TV show, and to the astronomical tradition of naming the first satellites of dwarf planets.

Based on spectral data, the researchers think Eris is covered with a layer of methane that has seeped from the interior and frozen on the surface. As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation, causing the methane layer to redden. But the methane surface on Eris is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Eris is farther from the sun.

Brown, Trujillo, and Rabinowitz first photographed Eris with the Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of 2005.

PASADENA, Calif.—The International Astronomical Union (IAU) today downgraded the status of Pluto to that of a "dwarf planet," a designation that will also be applied to the spherical body discovered last year by California Institute of Technology planetary scientist Mike Brown and his colleagues. The decision means that only the rocky worlds of the inner solar system and the gas giants of the outer system will hereafter be designated as planets.

The ruling effectively settles a year-long controversy about whether the spherical body announced last year and informally named "Xena" would rise to planetary status. Somewhat larger than Pluto, the body has been informally known as Xena since the formal announcement of its discovery on July 29, 2005, by Brown and his co-discoverers, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University. Xena will now be known as the largest dwarf planet.

"I'm of course disappointed that Xena will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision," said Brown. "It is scientifically the right thing to do, and is a great step forward in astronomy.

"Pluto would never be considered a planet if it were discovered today, and I think the fact that we've now found one Kuiper-belt object bigger than Pluto underscores its shaky status."

Pluto was discovered in 1930. Because of its size and distance from Earth, astronomers had no idea of its composition or other characteristics at the time. But having no reason to think that many other similar bodies would eventually be found in the outer reaches of the solar system—or that a new type of body even existed in the region—they assumed that designating the new discover as the ninth planet was a scientifically accurate decision.

However, about two decades later, the famed astronomer Gerard Kuiper postulated that a region in the outer solar system could house a gigantic number of comet-like objects too faint to be seen with the telescopes of the day. The Kuiper belt, as it came to be called, was demonstrated to exist in the 1990s, and astronomers have been finding objects of varying size in the region ever since.

Few if any astronomers had previously called for the Kuiper-belt objects to be called planets, because most were significantly smaller than Pluto. But the announcement of Xena's discovery raised a new need for a more precise definition of which objects are planets and which are not.

According to Brown, the decision will pose a difficulty for a public that has been accustomed to thinking for the last 75 years that the solar system has nine planets.

"It's going to be a difficult thing to accept at first, but we will accept it eventually, and that's the right scientific and cultural thing to do," Brown says.

In fact, the public has had some experience with the demotion of a planet in the past, although not in living memory. Astronomers discovered the asteroid Ceres on January 1, 1801—literally at the turn of the 19th century. Having no reason to suspect that a new class of celestial object had been found, scientists designated it the eighth planet (Uranus having been discovered some 20 years earlier).

Soon several other asteroids were discovered, and these, too, were summarily designated as newly found planets. But when astronomers continued finding numerous other asteroids in the region (there are thought to be hundreds of thousands), the astronomical community in the early 1850s demoted Ceres and the others and coined the new term "minor planet."

Xena was discovered on January 8, 2005, at Palomar Observatory with the NASA-funded 48-inch Samuel Oschin Telescope. Xena is about 2,400 kilometers in diameter. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Xena is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope.

Brown and his colleagues in late September announced that Xena has at least one moon. This body has been nicknamed Gabrielle, after Xena's sidekick on the television series.

Xena is currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), which means that it is some nine billion miles away at present. Xena is on a highly elliptical 560-year orbit, sweeping in as close to the sun as 38 astronomical units. Currently, however, it is nearly as far away as it ever gets.

Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year revolution. This means that Xena is sometimes much closer to Earth than Pluto—although never closer than Neptune.

Gabrielle is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. Because of its small size, Gabrielle could be oddly shaped.

Brown says that the study of Gabrielle's orbit around Xena hasn't yet been fully completed. But once it is, the researchers will be able to derive the mass of Xena itself from Gabrielle's orbit. This information will lead to new insights on Xena's composition.

Based on spectral data, the researchers think Xena is covered with a layer of methane that has seeped from the interior and frozen on the surface. As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation, that have caused the methane layer to redden. But the methane surface on Xena is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Xena is farther from the sun.

Brown and Trujillo first photographed Xena with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of 2005.